Method and apparatus for measuring the slopes of electric pulses which may be accompanied by high-background noise

ABSTRACT

In order to measure the slopes of pulses which make up a signal which may be accompanied by high-background noise, a sawtooth wave of slope is generated. The sawtooth wave is generated in synchronism with each pulse of the signal and the amplitude of each pulse is continuously divided by the amplitude of the sawtooth wave.

Inventors Jacques Max Salnt-Egreve; Francis Merdrignac, Grenoble; JulesRatahiry, Grenoble, all of France Appl. No. 802,484 Filed Feb. 26, 1969Patented Nov. 30, 1971 Assignee Commissariat A LEnergle Atomique Paris,France Priority Mar. 1, 1968 France 142 15 1 METHOD AND APPARATUS FORMEASURING THE SLOPES 0F ELECTRIC PULSES WHICH MAY BE ACCOMPANIED BYHIGH-BACKGROUND NOISE 11 Claims, 6 Drawing Figs.

IAIN/B/T [52] US. Cl 324/77 R, 235/196, 307/231, 328/161, 351/7. 324/140[51] lnt.Cl 1.G01n 23/16 [50] Field oiSearch 324/77, 99 D, 140; 235/196;351/7, 1;328/161, 114, 132; 307/229, 231; 128/206, 2.1

[56] References Cited UNITED STATES PATENTS 3,024,999 3/1962Heacock,Jr 1. 235/196 Primary ExaminerEdward E. KubasiewiczAttorney-Craig, Antonelli and Hill ABSTRACT: In order to measure theslopes of pulses which make up a signal which may be accompanied byhighbackground noise, a sawtooth wave of slope is generated. Thesawtooth wave is generated in synchronism with each pulse of the signaland the amplitude of each pulse is continuously divided by the amplitudeof the sawtooth wave.

AMPLIFIER EECGRDER METHOD AND APPARATUS FOR MEASURING THE SLOPES OFELECTRIC PULSES WHICH MAY BE ACCOMPANIED BY HIGH-BACKGROUND NOISE Thepresent invention is directed to a method and a device for measuring theslope of pulse phases which each exhibit a substantially linear rise ina pulse train constituting an electric signal which may be accompaniedby a very high level of background noise. One important application ofthe invention among many others consists in the utilization of signalsrepresenting physiological parameters for the purpose of bringing outthe most important characteristics.

One known method which is already employed for the purpose of measuringthe slope of an electric signal whose amplitude varies substantially ata linear rate in time consists in differentiating said signal in asuitable circuit. In practice, this solution is no longer acceptablewhen the slope is low, that is to say when the amplitude of the signalvaries slowly in time and/or when the useful signal is superimposed on ahigh background noise.

The present invention is directed to the basic concept of a method anddevice for measuring pulse slope in which the disadvantages of the usualmethods are reduced to a considerable extent and which, in particular,are not subject to the limitations referred to above.

With this objective, the invention proposes a method of measurement ofthe slope of electric pulses constituting a signal which is accompaniedby a high background noise, wherein said method consists in generating asawtooth wave of known slope at the instant of appearance of each pulseand in dividing the amplitude of said pulse by the amplitude of thesawtooth wave at the same instant.

The invention also proposes a slope-measuring device for the applicationof the method aforesaid. Further arrangements which are also provided bythe invention can advantageously be combined with the preceding but canalso be employed separately. These arrangements will be more clearlybrought out by the following description of one form of execution of theinvention corresponding to a particular application which is givensolely by way of nonlimitative example and which consists of a devicefor studying nystagmic jerks of the eyeball. The description refers tothe accompanying drawings, wherein:

FIG. 1 is a diagram showing the shape of the variation in time of thenystagmic signal (curve A), of the same signal after centering (curveB), of the superimposed sawtooth signal (curve C) and of the ratio ofthe signals (curve D);

FIG. 2 is a highly diagrammatic block diagram of the device forsupplying the slope ratio;

FIG. 3 is a block diagram of a circuit which can be incorporated in thedevice of FIG. 2 for supplying additional characteristics of the signal;

FIG. 4 is a diagram showing the variation in time of the signalsemployed in the circuit of FIG. 3;

FIG. 5 is a possible diagram of the measurement utilization circuit ofFIG. 2;

FIG. 6 is a diagram which is similar to FIG. 4 showing the shape of thesignals which appear in the circuit of FIG. 5.

Before describing the method and device according to the invention, itmay prove useful to recall the nature of nystagmic jerks and the objectof their study.

If periorbital cutaneous electrodes are applied to a patient who issubjected to periodic excitation (usually a pendular motion imparted tothe patient by means of an armchair in which the patient is supported),a so-called nystagmic signal is collected. This signal is made up of aseries of pulses, each pulse having a so-called slow phase with a smallangle of slope which is approximately constant and a return phase havinga steep slope. The polarity of the signal is reversed with the directionof rotation of the armchair The appearance of a series of pulsescorresponds to a reversal of motion of the armchair and the first slowphase has the smallest angle of slope. At the time of stopping prior toreversal of the direction of rotational motion of the chair, there is aperiod in which no significant pulses appear.

The curve A which is given in FIG. I shows a first period T in whichthere appear four pulses corresponding to the rotation of the chair inone direction followed by a period T which is devoid of characteristicsignals, then by a period T (corresponding to a rotation in the oppositedirection) comprising signals whose slow phases are of opposite slopewith respect to the slope of the pulses of the period T The pulses whichare recorded and which correspond to nystagmic jerks of the eyeballconstitute an important element of vestibular exploration. Thelow-gradient" phase of each pulse is the phase which corresponds withthe highest accuracy to the excitation which is derived from thelabyrinth and proceeds towards the nerve centers while thehigh-gradient" phase has a much more complex interpretation. It hasbecome apparent that the following rank among the most characteristicparameters: the mean angle of slope of the lowgradient or slow" phases,the mean value of these angles of slope as determined over a givenperiod of time, and the number of pulses (corresponding to the number ofnystagmic jerks) with either polarity during a given time interval.

The device which will now be described is intended to perform thefunctions mentioned above. It will readily be appreciated that, in theachievement of this objective, the design and development of a devicewhich permits the extraction of the parameters referred to give rise toa number of problems:

the signal has a high level of background noise which prevents directmeasurement by differentiation;

the presence of pulses in one direction and in the other-some slowphases can have a slope which is close to that of the fast-return"phases of pulses of opposite direction-entails the presence of circuitswhich make it possible to discriminate between the slow phases and thefast-return phases. As will be seen later, this discrimination utilizesthe presence of time intervals during which no signal to be processedappears between two pulse trains of opposite polarity.

The basic principle of the invention is as follows: a ratio isestablished between the amplitude of the slow phase and that of asawtooth wave which is a linearly increasing function-of time, thesawtooth wave being reduced to a zero or to a very small value as aresult of the fast return which follows a lowgradient phase. Theamplitudes are expressed as an electrical quantity which is usually avoltage.

In other words, there is effected a calculation of x (l) as defined by:

wherein:

wherein the second term is very small compared with the first.

The division can evidently be performed continuously point by point inanalog form or, after coding, in digital form.

The device in accordance with the invention as illustrated in FIG. 2 maybe regarded as comprising a parameter extraction circuit and aninhibition circuit which will be described in turn.

The signal which is taken directly from electrodes or preprocessed in aknown device is applied at 10 to the input of the two circuits.

The inhibition circuit is composed of two identical arms 12 and 12' toeach of which is assigned one pulse polarity: the arm 12, for example,comprises a differentiator 14 for the fastretum of positive pulses, saiddifferentiator being provided with an inhibition input 16. The presenceof a voltage at said input blocks the output 18 of the differentiator.This output 18 supplies a shaping circuit 20 which is connected on theone hand to one input of an OR- circuit 22 whose function will becomeapparent later and, on the other hand, to a measurement-permissioncircuit 24. This circuit 24 is of complex structure and must ensurethat:

when a first pulse is applied to the input of the circuit 24, said pulsecauses the emission at one output 26 of a voltage square wave having atime duration 1 I second, for example) which is adjustable by theoperator (this input being shown diagrammatically by the arrow 28) butdoes not result in the appearance of a signal at a second output 30which is connected to the input I6 ofthe difierentiator 14';

if a further input pulse which is separated from the first by a timeinterval less than 1- (that is to say prior to the end of the squarewave) is applied to the input, said pulse lengthens the square wave by aperiod equal to 7' and initiates at the output 30 the emission of asquare wave having a duration equal to the time which elapses betweenthe initial nystagmus and the final nystagmus as increased by the value7; this square wave serves to inhibit the differentiator 14' whichselects the negative pulses.

A number of different solutions are evidently open to selection in thedesign of the measurement-permission circuit 24. For example, it wouldbe possible to adopt a circuit arrangement of the type showndiagrammatically in FIG. which comprises:

a monostable circuit 80 controlled by means of a gate 82 of thefield-effect transistor type, the control electrode of which isconnected to the output of the circuit 20. This circuit 80 has twooutputs 26 and 27;

an amplifying and shaping stage 84 which is coupled to the output 27 ofthe monostable circuit 80;

a trigger circuit for positive signals 86 and coupled to the output 27;

an amplifying and shaping stage 88 which is coupled to the output ofthetrigger circuit 86;

a logic state storage device 90, the two inputs of which are coupled tothe gates 89 (output of stage 84) and 91 (output of stage 88) and whichsupplies the output 30.

The monostable circuit 80 which is shown in the figure is constituted bytwo transistors 92 and 94, the collector of the transistor 92 beingconnected to the base of the transistor 94 via the capacitor 96. Saidcircuit produces a square wave having a duration 0' ifit is driven by asingle pulse.

In the quiescent state, the transistor 94 is conducting and thetransistor 92 is blocked. The first pulse which is derived from theshaping circuit 20 blocks the transistor 94 and makes the transistor 92conducting by applying to the base of transistor 94 the positive voltageof the source +P. The collector of the transistor 92 then changes overfrom the voltage P to a zero voltage.

The second pulse again applies to the voltage +P to the base of thetransistor 94 and recharges the capacitor 96 at the voltage P; thecurrent which serves to recharge the capacitor 96 flows through theresistor 98 which connects the collector of the transistor 92 to thevoltage source P. This current produces at the point 27 a positivevoltage peak and causes the lengthening of the square wave derived fromthe monostable circuit 80 for the time duration 0.

The same process is repeated in the case of the other incident pulseswhich arrive at an instant corresponding to a time interval of less thana after the preceding pulses. There is collected at the output 26 asquare wave having opposite polarity with respect to the square wavewhich appears at 27 and has no voltage peaks, which corresponds whollyto the definition given earlier.

The gate 84 delivers at 89 a square wave having the same polarity as thesquare wave which appears at 27 and which is also free from voltagepeaks.

The circuit 86 operates as follows: as long as the signal at 27 iseither negative or zero, the first transistor is blocked and the secondtransistor 102 is in the conducting state: the output of the circuit isat a potential in the vicinity of zero.

When a positive peak arrives at 27, the transistor I00 becomesconductive and brings the output to a positive potential in the vicinityof +P. The stage 88 reverses the polarity of the pulses thus obtained.The logic state storage device 90 receives from the output 89 a trippermission signal in the form of a positive square wave; when this pulseis present, the device remembers" or stores the first pulse which isderived from the output 9! and is reset at the end of the square wavewhich is emitted at the output 89.

The shape of the signals which appear at the different points of thecircuit 24 given in FIG. 5 is illustrated in FIG. 6: the curve I showsthe signals at the output 20, the curve K shows the pulses which aredelivered at the output 27 of the monostable circuit each time a pulseof the curve J appears in less than a time interval 0' after thepreceding and the negative voltage which appears at the end of a timeinterval 0' after final pulse. The curves L, M and N show the voltagesat the outputs 26, 89 and 91 and it can be seen that there appears onthe curve M a period (shaded portion) during which the logic storagedevice is permitted to trip followed by a reset. Finally, the curve 0shows the voltage at the output 30 and the shaded zone corresponds tothe period of inhibition of the channel I2.

The operation of the inhibition circuit is apparent from FIG. 2: thefirst pulse of a series (separated from the last pulse of the precedingoutput by a time interval which is longer than 0') appears whereasneither of the two arms is inhibited. Said first pulse is selected byone of the arms 12 and I2 without any risk or error since it alwaysbegins with a slow phase. If the pulse is assumed to be positive, asquare wave appears at the output 26. When a second pulse arrives at theend of a time interval which is shorter than 0' said second pulse causesthe appearance of a square wave at the output 30 and the inhibition ofthe differentiator 14'; the arm 12 is thus inhibited throughout theseries ofpositive pulses.

The duration of the time interval 0' is evidently chosen so as to beshorter than T (FIG. 1): a duration of the order of one second isusually satisfactory.

The slope detennination circuit is composed of a centering unit 32, asawtooth wave generator 34 providing a known slope awhich may be varied,an analog divider circuit 36 and logic control circuits. The sawtoothgenerator 34 is triggered by the OR-circuit 22 and is blocked when it isno longer supplied with current. In other words, the return of thepulses effects the calibration of the sawtooth waves (curve C of FIG.I). It should be noted that the saw teeth start from a slightly positivevoltage K( formula 1). The generator 34 can consist of any conventionalcircuit. The so-called bootstrap generator which employs a normallyblocked field-effect transistor as a switching unit is eminently suitedto this purpose. A description ofa circuit ofthis type can be found inthe literature.

The centering unit 32 is supplied directly from the input 10 and resetat a zero output voltage when its control input 38 receives a signalfollowing each fast return. This signal is supplied in the followingmanner (with the reference to FIG. 2): the OR-circuit 22 for triggeringthe sawtooth waves and a second OR-circuit 22' which is coupled to theoutputs 26 and 26 (and which therefore delivers a voltage as long as oneof the circuits 24 and 24 emits an inhibiting square wave) are coupledto the inputs ofan AND-circuit 40. This circuit transmits to the input38 a reset pulse to the input 38 at the beginning of each nystagmicpulse of a series.

The pulses which pass out of the centering unit 32 (curve B of FIG. I)and which are identical in shape with the initial pulses but with anorigin which is reset to zero are applied to one of the inputs of adivider 36. The other input receives the sawtooth waves (curve C ofFIG. 1) of the generator 34.

Various types of analog dividers may be employed. For example, use canbe made of a circuit assembly comprising an operational amplifier, thenegative feedback loop of which is constituted by anamplitude-modulation and duration-modulation multiplier. Thus, thesignal to be processed is applied to the multiplier while the sawtoothwaves are applied to the input which is maintained at zero potential. Aprecision of the order of l in the division is thus readily achieved.

The device shown in MG. 2 comprises at the output of the divider 36 anamplifier 42 which supplies an analog recorder 44, said recorder beingalso supplied from the output via line 46 of the AND-gate 50. A timedelay is thus introduced in the triggering of the amplifier 32 withrespect to the appearance of the corresponding sawtooth. Thus, theoutput square waves of the amplifier t2 (curve D in H6. ll) appear onlyafter the period of time in which the approximation made for themeasurement of the slope is not permissible: this period of time appearson the curve D in the form of an interval between successive squarewaves. The recorder can be of a standard galvanometer type wherein theslope of each pulse will be represented by a square wave having aduration which is slightly shorter than that of the nystagmic jerk andthe amplitude and polarity of which indicate the value of the slope andits sign.

There can be added to the basic circuit shown in H6. 2 assemblieswhereby the mean value of the slopes of the slow phases of nystagmicjerks can be supplied directly as calculated either on the basis of agiven number of jerks or on the basis of a given time interval, such as,for example, a halfperiod of oscillation of the armchair correspondingto a same polarity of the jerks. It is possible for this purpose toutilize the circuit which is shown in MG. 3, the input 43 of which iscoupled to the output of the amplifier 42.

The principle of measurement of the mean value of slopes is as follows:the voltage square waves delivered by the amplifier 42 are converter tosquare-topped pulses having a constant predetermined duration and anamplitude which is proportional to the slope, said pulses beingtransmitted to a storage analog divider or, after summation of theamplitudes, the contents of the storage device are divided by the numberof square waves (that is to say the number of jerks).

The device which is represented in H6. 3 comprises a true delay line 50which is supplied from the input 418: a square wave applied to the inputfrom the instant t to the instant t,(curve E in FIG. 4) is delayed(curve F) by a time interval A! A! =1 00 sec., for example) without anychange in amplitude. The square waves are also applied to a control armcomprising a differentiator 52 which supplies a control peak at eachtrailing edge of a square wave (instant 1,). Said control peak triggersa monostable multivibrator 54 which delivers a control square signalhaving a duration at which is distinctly shorter than At. An extractioncircuit 56 which is supplied by the time-delay circuit 50 and controlledby the monostable multivibrator 54 delivers at its output 58 a squaresignal having a length E! and an amplitude which is proportion to thatof the input square wave in the delay line 50 (curve H). The extractioncircuit 56 is advantageously constituted by a linear gate comprising aninput field-effect transistor which therefore has a high inputimpedance.

The output 58 of the extraction circuit 56 is applied to an integratingcircuit 60 which sums the amplitudes and supplies at its output 62 avoltage which is proportional to the sum of the slopes from the time ofprevious resetting effected by applying a pulse to an input 63.

The device also comprises-a circuit for counting the number of nystagmicjerks consisting of a counter 64 (three decades are usually sufiicient),said counter being supplied by peaks which are each representative ofone jerk: the counter 64 can be supplied, for example, from the outputof the differentiator 52. The counter 64 can be of any conventional typesuch as, for example, a counter of the bistable circuit type. Thedigital output of said counter is transmitted to a digital-analogdecoder 66 which supplies a voltage proportional to the number ofjerks.

ln this manner, the ratio of the voltage representing the sum of theslopes (applied through the output 62) to the voltage representing thenumber of jerks is thus established by means of an analog divider 68 atinstants which are determined by application of a setting-up order to aninput 74. The mean slope is thus obtained at the output 70 and writtenin a recorder '72.

The recording operation which is carried out upon receipt of thesetting-up order which is applied to the input 72 of the divider isfollowed by an order for zero resetting of the integrator tit) and thecounter 64 (the input being shown in chain-dotted lines in FIG. 3).

The number of jerks can be placed in the recorder 72 at the same time asthe mean value of the slopes simply by simultaneous writing of theoutput voltage of the decoder 66. A conventional two-channel recorder ofthe galvanometer type can be employed for this purpose. Thus, one of thegalvanometers will receive the voltage which is applied through theinput 70 and which represents the mean value of slope while the othergalvanometer will receive a voltage which is proportional to the numberof jerks derived from the decoder 66.

The device of H68. 2 and 3 can further be completed by a countingcircuit serves to determine the number of jerks which take place bothtowards the right-hand side and lefthand side during each period ofoscillation of the pendular armchair in which the patient is seated.This parameter is sometimes of interest for the correct interpretationof nystagmus.

The counting circuit can be of very simple design. The circuit shown indashed lines in FIG. 3 is provided at the output of the differentiator52 with a switching unit 78 which, depending on their sign, directs theoutput pulses from the differentiator 52 towards either of the twochannels 76 and 76 which are each constituted by one counter. Othersolutions could be contemplated: it would thus be possible to employ asingle counter followed by a buffer storage device which, after eachcount in a given direction, receives the indications contained in thecounter and frees this latter for the following count. In all cases,setting-up can be effected in digital form by controlling by means of anauxiliary program the printing of indications contained in the counteror alternatively in analog form by digital-analog decoding (whereuponthe writing operation is no longer carried out in the form of a printedimpression but in the form of a graphic recording).

The invention is evidently not limited to the form of execution whichhas been illustrated and described by way of example and it will bereadily understood that the scope of this patent extends to alternativeforms of either all or part of the arrangements herein described whichremain within the scope of equivalent means as well as to any unit forthe practical application of the invention such as a device forprocessing physiological signals.

What we claim is:

l. A method of measurement of the slope of electric pulses constitutinga signal which may be accompanied by a high background noise, whereinsaid method comprises the steps of:

generating a sawtooth wave having a known slope in snychronism with eachof said pulses and of continuously dividing the amplitude of each ofsaid pulses by the amplitude of the sawtooth wave, whereby a ratiosignal, representative of the slope of each of said electric signalsbeing measured, is obtained.

2. A device for measuring the slope of electric pulses constituting asignal which may be accompanied by a high background noise comprising agenerator for producing sawtooth waves of constant and known slope,means for triggering said generator in response to a pulse whose slopeis to be measured and an analog dividing circuit which receives thepulse to be measured and the sawtooth wave which is delivered from thegenerator, whereby a ratio signal, representative of the slope of eachof said electric pulses measured, is obtained.

3. A device is accordance with claim 2, wherein said device comprises adifferentiating circuit to which said signal is applied, the output ofsaid circuit being coupled to the control input of the sawtooth wavegenerator in order to release said generator in response to a transientportion of a pulse.

4. A device in accordance with claim 2 wherein said device comprises twoseparate differentiating circuits each responsive to one polarity ofsaid pulses, the output of said circuits being coupled to the controlinput of the sawtooth wave generator in order to release said generatorin response to a transient portion of a pulse.

5. A device in accordance with claim 4, wherein each differentiator isassociated with a permission circuit for supplying an inhibition signalto the other differentiator for a predetermined time-duration after theemission by the first differentiator of a peak corresponding to saidtransient portion, said time-duration being shorter than the timeinterval which elapses between two pulse trains of opposite polarity.

6. A device in accordance with claim 2, wherein said device comprises acircuit disposed in the path of transmission of said pulses to saiddivider for zero resetting of the origin of the pulses.

7 A device in accordance with claim 2, wherein said device alsocomprises a circuit supplied by said divider for calculating the meanvalue of pulse slopes over a predetermined period.

8. A device in accordance with claim 7, wherein said device comprises acircuit for counting said pulses during said period of time.

9. A device in accordance with claim 8, wherein said circuit forcalculating the mean value of pulse slopes comprises a shaping stage forgenerating in respect of each pulse a signal of fixed duration having anamplitude which is proportional to the slope, an integrator connected tothe output of said shaping stage and a divider connected to theintegrator and to the counter circuit.

10. A method of measuring the slopes of a train of pulses within asignal each of said pulses being comprised of a first portion having asubstantially constant slope and a second portion, the absolute value ofthe slope of said second portion of each signals being smaller than theabsolute value of the slope of said first portion, comprising the stepsof:

differentiating each of said pulses:

generating a sawtooth signal, in synchronism with each of said pulses,the period of each sawtooth increment corresponding to the period ofeach of said first and second portions of each of said pulses; and

continuously dividing the amplitudes of each of said pulses by theamplitude of said sawtooth signal, to provide a ratio signalrepresentative of the slopes of said train of pulses.

11. A method in accordance with claim 10, further including the stepsof:

transforming said train of pulses into first and second respectivesequences of pulses of opposite polarity with intervals of time betweenpulse in each sequence during which no pulses occur; and

delaying one of said sequences of pulses with respect to the othersequence for a period of time shorter than the duration of each pulse inthe other sequence.

1. A method of measurement of the slope of electric pulses constitutinga signal which may be accompanied by a high background noise, whereinsaid method comprises the steps of: generating a sawtooth wave having aknown slope in snychronism with each of said pulses and of continuouslydividing the amplitude of each of said pulses by the amplitude of thesawtooth wave, whereby a ratio signal, representative of the slope ofeach of said electric signals being measured, is obtained.
 2. A devicefor measuring the slope of electric pulses constituting a signal whichmay be accompanied by a high background noise comprising a generator forproducing sawtooth waves of constant and known slope, means fortriggering said generator in response to a pulse whose slope is to bemeasured and an analog dividing circuit which receives the pulse to bemeasured and the sawtooth wave which is delivered from the generator,whereby a ratio signal, representative of the slope of each of saidelectric pulses being measured, is obtained.
 3. A device in accordancewith claim 2, wherein said device comprises a differentiating circuit towhich said signal is applied, the output of said circuit being coupledto the control input of the sawtooth wave generator in order to releasesaid generator in response to a transient portion of a pulse.
 4. Adevice in accordance with claim 2 wherein said device comprises twoseparate differentiating circuits each responsive to one polarity ofsaid pulses, the output of said circuits being coupled to the controlinput of the sawtooth wave generator in order to release said generatorin response to a transient portion of a pulse.
 5. A device in accordancewith claim 4, wherein each differentiator is associated with apermission circuit for supplying an inhibition signal to the otherdifferentiator for a predetermined time-duration after the emission bythe first differentiator of a peak corresponding to said transientportion, said time-duration being shorter than the time interval whichelapses between two pulse trains of opposite polarity.
 6. A device inaccordance with claim 2, wherein said device comprises a circuitdisposed in the path of transmission of said pulses to said divider forzero resetting of the origin of the pulses.
 7. A device in accordancewith claim 2, wherein said device also comprises a circuit supplied bysaid divider for calculating the mean value of pulse slopes over apredetermined period.
 8. A device in accordance with claim 7, whereinsaid device comprises a circuit for counting said pulses during saidperiod of time.
 9. A device in accordance with claim 8, wherein saidcircuit for calculating the mean value of pulse slopes comprises ashaping stage for generating in respect of each pulse a signal of fixedduration having an amplitude which is proportional to the slope, anintegrator connected to the output of said shaping stage and a dividerconnected to the integrator and to the counting circuit.
 10. A method ofmeasuring the sloPes of a train of pulses within a signal, each of saidpulses being comprised of a first portion having a substantiallyconstant slope and a second portion, the absolute value of the slope ofsaid second portion of each of said signals being smaller than theabsolute value of the slope of said first portion, comprising the stepsof: differentiating each of said pulses: generating a sawtooth signal,in synchronism with each of said pulses, the period of each sawtoothincrement corresponding to the period of each of said first and secondportions of each of said pulses; and continuously dividing theamplitudes of each of said pulses by the amplitude of said sawtoothsignal, to provide a ratio signal representative of the slopes of saidtrain of pulses.
 11. A method in accordance with claim 10, furtherincluding the steps of: transforming said train of pulses into first andsecond respective sequences of pulses of opposite polarity withintervals of time between pulse in each sequence during which no pulsesoccur; and delaying one of said sequences of pulses with respect to theother sequence for a period of time shorter than the duration of eachpulse in the other sequence.